Apparatus for coating traveling webs



De. 30, 1969 G. K. HUNGER 3,485,482

APPARATUS FOR COATING TRAVELING WEBS Filed Dec. 30, 1966 4 Sheets-Sheet1 FIG. I.

FRESH COAT/N6 I NVEN T OR. Gunther K. Hunger ATTORNEY Dec. 30, 1969 G.K. HUNGER 3,486,482

APPARATUS FOR COATING. TRAVELING WEBS Filed Do. so, 1966 4 Sheets-Sheet2 A (1) N\ r I INVENTQR Gunther K. Hunger ATTORNEY G. K. HUNGERAPPARATUS FOR COATING TRAVELING wEias Dec. 30, 1969 4 Sheets-Sheet 5Filed Dec. 30, 1966 R O T N M Gunther K. Hunger BY Y.

ATTORNEY Dec. 30, 1969 G, K] HUNGER 3,486,482

APPARATUS FOR COATING TRAVELING WEBS Filed Dec. 30, 1966 4 Sheets-Sheet4 P O i IN VENTOR. Gunther K. Hunger wy/Mm;

A TTORNE Y United States Patent 3,486,482 APPARATUS FOR COATINGTRAVELING WEBS Gunther K. Hunger, Ellicott City, Md., assignor toWestvaco Corporation, a corporation of Delaware Filed Dec. 30, 1966,Ser. No. 606,164 Int. Cl. B05c 11/02, 3/02 US. Cl. 118-603 6 ClaimsABSTRACT OF THE DISCLOSURE This invention relates to the application ofcoatings to traveling webs such as paper, paperboard, and the like. Moreparticularly, the invention relates to apparatus for coating a travelingweb in such manner that coating is forced into the web, as well asmetered thereon, as the result of the combined use of a coatingimpelling nip and a pressurized pond of coating.

The coating of web material, such as paper and paperboard, may beperformed in general by the use of roll coaters, air knife coaters, orblade coaters. It is known that with pond type blade coaters, such asshown in United States Patent 2,368,176 to A. R. Trist, or with invertedblade coaters, such as shown in the United States Patent 3,149,005 to M.M. Brundige, a primary problem encountered is that of scratching orstreaking of the coated surface. The scratches or streaks are primarilycaused by hard particles in the coating which become lodged in the nipbetween the doctor blade and the traveling web, and as the web travelsunder and past the blade, the absence of coating on the web, caused bythe lodged particle, takes the form of a streak or scratch on the web.This streaking continues until either the particle becomes dislodged andpasses under the blade or until the particle is abraded away.

The particles which cause the streaking may be dried adhesive or driedcoating from the coating supply system or they may be foreign materialswhich have not been removed from the coating system. Screens normallyused in the industry to screen paper coatings are not fine enough toremove all scratch producing particles, and the use of finer meshscreens has not been found to be commercially feasible.

The coating apparatus of this invention readily minimizes the ability ofscratch producing particles to reach the doctor blade and causescratching, while at the same time, it applies higher coat weights thando conventional blade coaters under equivalent coating conditions. Thisis accomplished by a coating apparatus which includes a backing roll onwhich a traveling web may be caused to travel, a coating applicator panopposing a portion of the backing roll and sealed to the atmosphere atthe incoming web end, a first adjustable coating impelling and meteringdevice forming, preferably, a positive gap with the backing roll at theoutgoing web end of the applicator pan and a positive or negative gapwith the web, a second metering device spaced from the outgoing web endof the applicator pan, hydrostatic pressure means forcing coating intothe applicator pan and into the traveling web, and means for drainingfrom the applicator pan the scratch producing particles which gather inan area of low streaming velocity in the bottom of the pan.

3,486,482 Patented Dec. 30, 1969 ICC The present invention is based uponthe finding that a self-cleaning of the coating takes place in theapplicator pan of the present coater, such that most of the scratchproducing particles never reach the second, and final, metering device.This self-cleaning phenomenon is attributable to the action of the firstmetering device which impels coating into the web, and to flow streamswhich are set up in the coating pan. Scratch producing particles arecarried in the flow streams and are deposited in areas of lowerstreaming velocity within the applicator pan. The particles which gatherin the low velocity region in the bottom of the pan may be continuouslydrained from the same.

For the foregoing purpose, a coating reservoir is placed above theapplicator pan to provide hydrostatic pressure for supplying coating tothe pan and aiding in the forcement of coating into the web. Coating inthe pan is picked up by the web which moves with the rotating backingroll and passes through a first metering nip formed by the web and thecoating impelling device at the outgoing end of the applicator pan. Thecoating impelling device may be spaced from the web to form a gap ofsmall positive clearance between the device and the web or the coatingimpelling device may be adjusted to provide a negative clearance betweenthe web and the device. In any event, an excess of coating, as comparedto the desired final coat weight, is metered onto the traveling web bythe coating impelling device. Spaced from the outgoing web end of theapplicator pan is a second metering device which smooths the coating onthe web and meters the coating to the desired final coat weight. Thecoating impelling and metering device preferably is in the form of a barof rigid material and is adjustable toward and away from the web andbacking roll, to vary the gap between the device and the web. The secondmetering device preferably is a pneumatically loaded trailing blade.Means for draining scratch producing particles which gather in an areaof low streaming velocity in the applicator pan are provided, and meansfor raising and lowering the applicator pan are also provided.

This invention will be best understood by reference to the drawings, inwhich:

FIGURE 1 is a side elevation view of the coater and coating system ofthis invention;

FIGURE 2 is an expanded, more detailed view of the applicator pan andmetering devices shown in FIG- UREl;

FIGURE 3 is a perspective view of the coater of FIGURE 1;

FIGURE 4 is an end view of the coater of FIGURE 1 showing means foraltering the position of the applicator pan and final metering device.

Referring to FIGURES 1-3, the backing roll 10 may be of any suitablematerial but is preferably a resilient roll and is driven in thedirection of the arrows. A coating applicator pan, designated generallyas 12, is disposed beneath and adjacent to a portion of the backing roll10. The applicator pan 12 is comprised of a back member 14, a secondarybottom member 16 which extends from the back member 14 in the directionof the backing roll 10, a primary bottom member 18 which is locatedbetween the secondary bottom member 16 and the backing roll 10 andextends from the back member 14 in the direction of the backing roll 10to form a pond 13 for coating material, and side members 20 and 20',

Each side 20 and 20' of the applicator pan 12 is machined along most ofits top edge to fit the contour of the backing roll 10. Seals (notshown) of suitable material, such as Tefion, are suitably located on theinterior surfaces of the sides 20 and 20' and bear against the travelingweb W to prevent coating from leaking between the web W and sides 20 and20'.

As best illustrated in FIGURE 2, the ingoing web end of the applicatorpan 12 is sealed by blade 22 which is housed in blade holder 24comprising jaws 25 and 26 fastened to each other by threaded screws 27.The blade holder 24 is secured by threaded screws 28 to the top portionof the back member 14. Blade 22 extends from side 20 to side 20' andbears at its tip against backing roll 10 to seal the applicator pan 12.The outgoing web end of the applicator pan 12 is sealed by a coatingimpelling and metering device 29 which is preferably a rigid bar mountedby screws 30 on a flexible leaf spring 32 which is suitably attached atone end by screws 34 to the primary bottom member 18. Adjusting screws36 extend through the primary bottom member 18 and contact leaf spring32. Turning of screws 36 adjusts leaf spring 32 and the bar 29 toward oraway from the backing roll 10 to thereby control the amount of coatingwhich passes with the web W to the final metering station. For mostcoating operations, it has been found preferable to provide a smallpositive clearance between the backing roll 10 and the metering bar 29and to provide a small positive or negative clearance between themetering bar 29 and the web W. The web W and coating thereon passingbetween the metering bar 29 and the backing roll 10 seals the pond 13 atthe outgoing web end.

The final metering device takes the form of a trailing blade 40 suitablymounted in a blade holder 42 which is attached to a T-bracket 44 mountedfor rotation on cylinder 46. The bracket 44 carries a coating returnchannel member 48 which returns excess coating metered from the web byblade 40 to the coating return portion 50 of the applicator pan 12formed by the secondary bottom member 16, the back member 14, and theprimary bottom member 18. Trailing blade 40 is spaced from the outgoingweb end of the applicator pan 12, in the direction of rotation ofbacking roll 10.

The size of the applicator pan may vary as the size of the backing rollis varied. It has been found that a contact angle of at least ispreferred for best quality, regardless of the size of the backing roll,and contact angles of up to 180 are within the scope of this invention.The contact angle is the number of degrees of backing roll circumferencewhich is in contact with the applicator pan at one time, i.e., thatportion of the backing roll 10 between sealing blade 22 and metering bar29.

In one embodiment of the invention, coating material from fresh coatingfeed line 69 and from conduit 67 is moved by pump 70 to tank 52 viaconduit 71, valve 73, and conduit 72. Tank 52, which is equipped with anoverflow conduit 75, is located above the applicator pan 12 to providehydrostatic pressure. The coating material flows by gravity from tank52, through conduit 54 to coating distributor 56 which is suitablysecured to the back 14 of the applicator pan 12. Valve 58 controls theflow of coating from tank 52 to the applicator pan 12. By varying theheight of tank 52 above the applicator pan 12, the hydrostatic pressureis varied, becoming less when the tank is lowered and more when it israised. Conduits 54, 58, 67, 71, 72, and 74 are preferably flexible toallow for varying the height of tank 52 above the applicator pan 12.

In another embodiment of the invention, coating material is suppliedunder hydrostatic pressure to applicator pan 12 by means of the deliverypump 70. Three-way valve 73 is set to close conduit 72 and directcoating material from pump 70, through conduits 71 and 74 to conduit 54,tank 52, and distributor 56, and into applicator pan 12. That portion ofconduit 54 which is above conduit 74, as well as tank 52, functions as astandpipe to maintain the coating material in the applicator pan 12under relatively constant pressure, i.e., the standpipe buffers againstany surges in the delivery of coating to pan 12 which may be attendantwith the use of a pulsating pump 70. In this connection, conduit 58 maybe used as 4- a standpipe, in this embodiment of the invention, withoutthe necessity of employing a tank such as tank 52.

The back 14 of applicator pan 12 is slotted across its width asindicated by inlets 59. Coating material flows through distributor 56,through inlets 59 in the back member 14, and into the applicator pan 12.The applicator pan 12 is completely filled with coating material duringoperation of the coater, and the coating in the pan 12 is underhydrostatic pressure due to the gravity feed of coating from theelevated tank 52 or from its action as a standpipe, depending upon whichembodiment of the invention is employed.

Maintaining the coating in pan 12 under pressure is an important featureof the present invention. By employing a hydrostatic head to pressurizethe coating in pan 12, high coat weights are achieved by the pressurizedcoating being driven into the traveling web W. Further, the hydrostaticpressure cooperates with the coating impelling bar 29 to force coatinginto the web and through the nip between the impeller 29 and the web W,resulting in the production of high coat weights and a smooth and glossycoated product. It has been found that a web of paper is smoother beforeentering a pond of coating than it is after leaving the pond because theweb swells in the pond and surface roughness increases. It is myunderstanding that the impelling bar 29 of the present invention smoothshigh points of the swollen web as well as forces coating into the lowareas of the web, to thereby produce a coated product with moresmoothness and gloss than heretofore produced by known blade coaters.

As the web travels around backing roll 10, excess coating is meteredfrom the web to the desired final level by blade 40. The excess coatingis directed by channel member 48 to the coating return portion 50 of theapplicator pan 12, and the coating in the coating return 50 is drainedthrough conduit 60 to screen 62. Conduits 64 are provided to drainscratch producing particles which collect in the pond 13 of applicatorpan 12 during operation of the coater. Valves 66 control this drainingoperation and are normally set in a slightly open position in order toallow the particles which settle in the primary low velocity area A2 inpond 13 to be bled off continuously.

All return coating material from conduits 60 and 64 passes throughscreen 62 and the rejected material subsequently is removed from thecoating system through conduit 68. Acceptable coating material passingthrough screen 62 is moved by pump 70 through conduits 71 and 72 tocoating supply tank 52 for reuse or is delivered by pump 70 directly tothe applicator pan 12.

In the operation of the device, which finds great utility in the coatingof paper and paperboard webs, a web W passes partially around thebacking roll 10 which is rotating at web speed. The web, which is widerthan the width of the applicator pan, passes between the backing roll 10and sealing blade 22 and is contacted by coating material in the pond 13of applicator pan 12. The web W passes through pond 13, picking upcoating material from the pond, to metering bar 29 which impels coatingmaterial into the web due to the localized higher hydrostatic pressurethat exists in the nip between bar 29 and web W. As the web W passes bar29, an excess of coating in layer-form is metered onto the web. The webW continues in its movement with'backing roll 10 to trailing blade 40which meters a final and smooth layer of coating on the web. The web Wthen leaves backing roll 10 at a suitable point and passes to dryingdevices, not shown.

The bottom of the pond 13 has been designed to create the area A2 oflower streaming velocity. This has been accomplished by forming an anglein the bottom of the pond 13 between bottom member 18 and back member 14as opposed to having the back and bottom members define a curvilinearconfiguration. In the drawings, the bottom member 18 and back member 14are shown as forming an approximate right angle but any angle whichcreates an area of lower streaming velocity may be employed.

During operation of the coater, movement of the backing roll and web Wcreates flow streams in the pond 13 of applicator pan 12 as illustratedin FIGURE 2 at 74, 75, 7-6, 77 and 78. Model studies have shown thatthere are two areas in the pond 13 where there is relatively littlecoating movement, and that contaminating particles tend to gather inthese regions. One such area is located at the center of the streamlines, indicated generally as A1, where some contaminating particlestend to gather. The other area of lower streaming velocity, A2, islocated in the bottom of the pond 13, where contaminating particles alsotend to gather. It has been found that the scratch level of the coaterof this invention is much less than conventional trailing or invertedblade coaters, especially when scratch producing particles, as theygather in area A2 are drained from pond 13. These scratch producingparticles are bled off through conduits 64 and are removed from thecoating system by screen 62.

As a specific illustration of a typical run with the coater of thisinvention, an aqueous coating composition comprising 100 parts pigment,16 /2 parts acrylic resin, and having a solids content of about 60%, wasprepared and utilized in the coater of this invention and in aconventional inverted blade coater of the type shown in U.S. Patent3,149,005. Blade loadings were identical in each coater and bladeconditions were also the same, being a .015" blade, 45 blade angle, andblade extension. The clearance between metering bar 29 and backing roll10 was set at .0015", and the contact angle (number of degrees ofbacking roll circumference between the pan sealing blade and themetering bar) was approximately 65. Both coaters were run at 400 feetper minute,

and the web material coated was 14 point paperboard. The followingresults were obtained:

Standard inverted Invention coater blade coater Blade load coat weight,coat weight,

(p.s.i. static) lbs/3,000 sq. ft. lbs/3,000 sq. ft.

It is seen that a higher coat weight is obtained with the coater of thisinvention at equal solids level of the coating and equal bladeconditions. Further, at equal coat weights, the invention coaterproduced a more glossy product. For example, the above-noted papercoated with 4.6 pounds of coating (invention coater) had a gloss of 31as measured according to Tappi Standard T480m-5 1, while the paper with4.4 pounds of the same coating applied by the standard inverted bladecoater had a gloss of only 25. Additional studies have shown that papercoated with the invention coater exhibits a Bekk smoothness of severalhundred units more than the same paper coated similarly by a standardinverted blade coater.

In another series of runs made with a coating composition similar to theabove, the scratch level of the coated paperboard was compared for thecoater of this invention and a standard inverted blade coater. The sameblade and metering bar conditions as above noted were utilized. Inaddition to the contaminants which are normally found in a paper coatingcomposition, sand was added to the coatings for each coater in order tomake a more drastic comparison between the scratch levels produced byeach coater, and further to illustrate the selfcleaning effect whichoccurs in the coater of this invention. The total number of scratchesfound on the coated web, per strip 100 ft. long and 10 inches wide, werecounted and the average results for four runs is shown below:

Number of Number of scratches scratches standard invention inverted Testcoater blade coater No contaminant added 3. 2 7. 3 gram of sand passing325 mesh screen added per gallon of coating- 16. 5 40 gram of sandpassing a 200 mesh screen but retained on a 325 mesh 32 5 334 screenadded per gallon of coating- As has been mentioned, and shown, thecoating impelling and metering device 29 preferably is in the form of apointed rigid bar and steel metering bars have been used. Other devices,such as a blade, a rod or wire wound rod rotating in a direction counterto backing roll rotation, maybe used as the impelling and meteringdevice, but itiihas been found that the steel bar produces a coatedproduct having the best quality and lowest scratch level.

The distance between the first metering nip and the trailing blade 40 ofthis invention should be designed at a minimum in order to preventdewatering of the film of coating between the first and second meteringdevices. Distances up to about six inches have been utilized with nosignificant quality losses. A distance of about three inches ispreferred.

Referring to FIGURE 4, means are illustrated for moving the applicatorpan 12 and blade 40. Such means are provided at each side of themachine. Backing roll 10 has a shaft 11 which is supported throughpillow block bearing by frame cap 81 mounted on frame member 82. Pivotarm 83, slotted at 8-4, is carried at one end on shaft 85 which isrotatively supported by bearing 86 secured to pivot arm bracket 87.Pivot arm 83 is secured at its other end to applicator pan 12. Pivot arm88, slotted at 89, is carried at one end on shaft 90 which is rotativelysupported by bearing 91 secured to pivot arm bracket 87. Pivot arm 88 issecured at its other end to applicator pan 12.

Hydraulic cylinder 94, which is securely mounted on frame members 82beneath the pan 12, has a piston rod 96 which cooperates with pivot arm83 by means of an extension shaft 98 which is housed in slot 100 ofpivotarm 83. The pan 12 may be retracted by the pivot armhydraulic cylinderarrangement for threading a traveling web around backing roll 10 or toclean the machine.

Blade cylinder 46 has a shaft 102 which is held by crank arm 104pivotally secured to piston rod 106 of pneumatic cylinder 108. Pneumaticcylinder bracket is mounted on frame member 82 and pneumatic cylinder108 is pivotally mounted on bracket 110- Blade cylinder bracket 112,mounted on frame member 82, rotatively carries shaft 102 by means ofbearing 114. Adjustment of the air pressure in pneumatic cylinder 108controls the degree of rotation of blade cylinder 46 to which blade 40is attached, and controls the pressure loading on blade 40 and the finalcoat weight metered thereby.

Other mechanisms for moving pan 12 and blade 40 may be employed, but itis preferred that blade 40 be pneumatically loaded for best qualityresults.

The novel coating apparatus of this invention has been run at speedsvarying from about 100 to 1800 feet per minute. The angle which blade 40makes with the tangent to the backing roll 10 at the point of bladecontact has been varied from about 20 to 70, with a preferred bladeangle of from 45 to 60. Coat weights from about 3 to 10 pounds per 3000square feet of web have been applied, and the clearance between backingroll 10 and metering bar 29 has been varied from a negative. clearanceof about .010" to a positive clearance of about .003", with thepreferred being a positive clearance of from .0015" to .003".

While preferred embodiments of the invention have.

been illustrated and described in detail, it is to be understood thatchanges may be made therein and the invention embodied in otherstructures. Hence, the present embodiments are to be considered asillustrative and not as restrictive, and it is intended to cover theinvention in whatever form its principles may be utilized.

I claim:

1. An apparatus for coating traveling webs which includes a rotating webbacking roll on which a traveling web is caused to travel, a coatingapplicator pan opposed to a portion of said backing roll for supplyingcoating material under pressure to the. traveling web, and a trailingblade opposed to the backing roll at a metering station which is spacedfrom said applicator pan in the direction of rotation of said backingroll, said coating applicator pan comprising a back member, primary andsecondary bottom members joined at one end to and extending from saidback member in the direction of the backing roll, said primary bottommember disposed between the backing roll and the secondary bottom memberand meeting with the back member angularly to form an area of lowstreaming velocity within the coating applicator pan adjacent thejointure of said back member and said primary bottom member, sidemembers attached to said back member and said bottom members, each sidemember being shaped along one edge to fit the. contour of the backingroll, said primary and secondary bottom members defining an open channelto receive excess coating material which is metered from the travelingweb by the trailing blade, sealing means mounted on said back member andextending longitudinally of said applicator pan and bearing against saidbacking roll for sealing the applicator pan to the atmosphere, a coatingimpelling and metering bar adjustably mounted on the primary bottommember of the applicator pan for impelling coating material into and formetering an excess of coating material onto the traveling web, saidcoating apparatus further including hydrostatic pressure means forcingcoating material into said applicator pan, means for draining coatingmaterial from said area of low streaming velocity within said applicatorpan, screening means through which drained coating material is passed toremove contaminant particles, and conduit means connecting the screeningmeans and the hydrostatic pressure means through which the coatingmaterial which passes through the screening means is returned to saidhydrostatic pressure means.

2. The apparatus of claim 1 in which the hydrostatic pressure meanscomprises a coating reservoir located at a variable height above saidapplicator pan, and conduit means connecting said coating reservoir andsaid applicator pan for delivering coating material under nonpulsatingpressure from said coating reservoir to said applicator pan.

3. The apparatus of claim 1 in which at least about 60 degrees of thecircumference of the backing roll is opposed by the applicator pan fromsaid sealing means to said metering bar.

4. The apparatus of claim 1 in which said trailing blade forms an angleof from about 20 to about 70 degrees with the tangent to the backingroll at the. point of blade contact.

5. In an apparatus for coating a traveling web of paper,

paperboard and the like comprising a web backing roll about which atraveling web is passed, a coating applicator pan opposed to a portionof the backing roll for supplying coating under pressure to the rollbacked web, sealing means at the incoming web end of the applicator panopposed to the backing roll to seal the pan to the atmosphere at saidincoming web end of the pan, pressure means forcing coating materialinto the applicator pan, a coating impelling bar adjustably mountedtoward and away from the backing roll at the outgoing web end of theapplicator pan for impelling coating material into the web, said coatingimpelling bar forming a positive gap with the backing roll through whichthe traveling web passes with a metered excess amount of coatingmaterial thereon, and a trailing blade opposed to the backing roll at ametering station which is spaced from said outgoing web end of theapplicator pan in the direction of rotation of the backing roll, theimprovement characterized by said applicator pan comprising a backmember, primary and secondary bottom members joined at one. end to andextending from said back member in the direction of the backing roll,said primary bottom member disposed between the backing roll and thesecondary bottom member and meeting with the back member angularly toform an area of low streaming velocity within the coating applicator panadjacent the jointure of said back member and said primary bottommember, side members attached to said back member and said bottommembers, each side member being shaped along one edge to fit thecontourof the backing roll, said primary and secondary bottom members definingan open channel to receive excess coating material which is metered fromthe traveling Web by the trailing blade, means for draining coatingmaterial from said area of low streaming velocity within said applicatorpan, screening means through which drained coating material is passed toremove contaminant particles, and conduit means connecting the screeningmeans and said pressure means through which the coating material whichpasses through the screening means is returned to said pressure means.

6. The apparatus of claim 5 in which the improvement is furthercharacterized in that said primary and secondary bottom members extendfrom said back member upwardly in the direction of the backing roll, andsaid primary bottom member meets said back member substantially at aright angle to form said area of low streaming velocity.

References Cited UNITED STATES PATENTS 2,796,846 6/1957 Trist 118413 X3,051,125 8/1962 Ahara et al. 118-603 3,079,889 3/1963 Jacobs et al.118413 X 3,179,536 4/1965 Matinek 118-407 X 3,192,895 7/1965 Galer118-413 X 3,354,867 11/1967 Pomper et a1 118126 X WALTER A. 'SCHEEL,Primary Examiner JOHN P. MCINTO'SH, Assistant Examiner US. Cl. X.R.118126, 413

